Transmission device with differential and coupling particularly for motor vehicles

ABSTRACT

According to the invention, an output element of a differential is made in two parts (14a, 14b), one (14b) of these two parts being axially mobile under the effect of a torque transmitted through this output element. This axial displacement is used to act either on a friction clutch or preferably on a coupling of the viscocoupler type in order to modify its characteristics. 
     Application particularly to motor vehicles.

The present invention relates to differential transmissions usedparticularly in motor vehicles.

These differentials comprise one input element and two output elementsmounted so that they rotate about the same axis, the two output elementsbeing connected, in one form of layout, to lateral propeller shaftsleading to the main wheels of the vehicle. In another configuration, thetwo output elements may be connected respectively to the input elementsof two other differentials.

Improvements have been sought in the operation of these differentials bycombining them with locking or slip-limiting devices.

A first type of self-locking differential comprises at least onefriction clutch interposed between two of the said input and outputelements, this clutch being controlled by at least one mobile elementinside the differential, the position of which depends on the torquewhich passes in transit through this differential.

A second attempt to improve the operation of a differential consisted inassociating it with a coupling device with discs and with a viscousfluid operating in shear ("viscocoupler"), interposed between two of thesaid input and output elements of the differential. In this second case,it is the difference in rotation speed between the two elements betweenwhich the viscocoupler device is interposed which determines the brakingefficiency of the said viscocoupler device.

These two types of device have disadvantages which result from the factthat in one case the clutch control in practice takes into account onlythe torques passing in transit through the differential and the sign ofthe difference in speeds between the output elements, while in thesecond case it takes into account only the difference in speeds betweenthe elements between which the viscocoupler device is interposed. Theresult is that, in both cases, there are unchangeable and henceunsuitable characteristics of the variation in torque as a function ofthe speed difference.

These disadvantages manifest themselves particularly, for the first typeof device, through difficulties with steering during parking manoeuvres,or else through the creation of torques, transferred between wheels orbetween axles, which are large and whose direction can change abruptly,even though the ground only allows weak driving or braking torques, andfor the second type through a certain deficiency in the use of antilockbrake control systems (ABS).

Patent Application FR-90 05 907 proposes a device which enables most ofthese disadvantages to be overcome and which has a wider range of usethan known devices. This application relates to a device consisting of adifferential comprising a housing, one input element and two outputelements, and a controlled-slip coupling device disposed between two ofthe said input and output elements; it is characterised in that thedifferential includes at least one element which is mobile under theeffect of an engine torque, the displacement of which is used to modifythe operational characteristics of the controlled-slip coupling device.

In a variant of the embodiment, the mobile element is an additionalinner housing sliding axially within the main housing and sets of rampsand pins provided, respectively, on the main and inner housings, makingit possible to obtain the axial displacement of the said inner housingduring a relative angular displacement between the two housings. Whenthe torque is an engine torque, the ramps act on the pins so as todisplace the inner housing in one direction. Stops are also provided sothat the two housings rotate solidly with each other during a torquefrom engine braking, without axial displacement of the inner housing.

Such solutions with an inner housing are satisfactory since they enablethe original clearances and gearing adjustments to be preserved. Theyare, on the other hand, expensive and bulky.

The objective sought here involves obtaining comparable results at lowercost and with less bulk.

To achieve this, the subject of the invention is a transmission device,particularly for motor vehicles, comprising a differential consisting ofa housing, one input element and two output elements, and a couplingdevice disposed between two of the said input and output elements, anoutput element of the differential with which the coupling devicecooperates being made in two parts, one of which carries teeth andcooperates with at least one other component of the differential, whilethe second is axially mobile over a predetermined distance, and issolidly attached to the rotation of an output shaft, means beingprovided between these two parts to allow a limited angular clearancebetween them and so that a relative angular displacement between thesetwo parts under the effect of a torque is reflected in an axialdisplacement of the said second part which acts on the coupling device,characterised in that the first part of the output element, whichcarries teeth, bears axially against a component itself fixed axially.

According to other characteristics:

the said first part bears against one face of the differential housing.

the said first part bears against one face of a pinion-holder formingpart of the differential.

the said means comprise sets of ramps inclined with respect to thedirection of the axis of the said output element, which cooperate witheach other when an engine torque passes in transit through thedifferential.

the said means also comprise sets of ramps which cooperate with eachother when a braking torque passes in transit through the differential.

the said output element is a side gear.

the mobile part of the side gear incorporates a sleeve connected bysplines to the output shaft.

the coupling device is a friction clutch and the mobile part of theoutput element acts in such a way as to control this clutch.

the coupling device is a viscocoupler and the mobile part of the outputelement acts in such a way as to alter the operational characteristicsof this viscocoupler.

The invention will be described in more detail below with reference tothe appended drawings, given solely as examples, and in which:

FIG. 1 is a partial longitudinal cross-sectional view of a transmissiondevice according to the invention;

FIG. 2 is a cross-sectional view through the line 2--2 of FIG. 1;

FIG. 3 is a partial longitudinal cross-sectional view of a variant ofthe embodiment;

FIGS. 4A and 4B represent two cross-sectional views through the line4--4 of FIG. 3 according to two variants of the embodiment;

FIG. 5 is a partial cross-sectional view of another variant;

FIG. 6 is a longitudinal cross-sectional view of another mode ofembodiment of the invention applied to a differential with an epicyclicgear train; and

FIG. 7 is a diagram illustrating the operation of a device according tothe invention.

In FIG. 1 can be seen a differential comprising a housing 10 which issolidly attached to a crown wheel 11 and which forms the input elementof this differential, this housing being mounted in such a way that itcan rotate, with respect to a supporting member 12, by means of bearings13 whose axes lie along X--X. Mounted within this housing in such a waythat they can rotate around the same axis X--X are two side gears 14, 15which constitute the output elements of the differential and which areconnected respectively to shafts 16 and 17. Moreover, the housingcarries at least one pinion-holding pin 18 on which are disposed sidepinions 19 whose teeth mesh with the side gears 14, 15.

The side gear 15 bears laterally in a standard manner against a face 20of the differential housing.

According to the invention, the side gear 14 is made in two parts 14a,14b. The first part 14a incorporates teeth 21 engaging with the teeth ofthe side pinions 19 and abuts a face 22 of the housing. The second part14b is solidly attached to the shaft 16 by means of splines 23 and it ismounted in such a way as to be capable of sliding along the direction ofthe axis X--X. The two parts 14a, 14b of the side gear incorporaterespectively sets of grooves 24 and teeth 25, preferably spacedregularly around the periphery of the sleeve 14b, which mark theboundaries of ramps 26, 27 which cooperate to produce an axialdisplacement of the sleeve 14b when a torque is in transit through thedifferential as shown in F1 of FIG. 2. The orientation and slope ofthese ramps are chosen in such a way that the sleeve 14b is displacedtowards the left when facing the drawing when an engine torque is intransit through the differential. The first part 14 a is not allowed tomove axially due to the abutment with face 22 and the meshing of gearteeth 21 with the teeth of the side pinions 19.

When the torque which is in transit through the differential correspondsto engine braking as shown in F2 of FIG. 2, it is ramps or stops 28, 29which are involved in transmitting this torque and, depending on theorientation of these ramps or stops, different operationalcharacteristics can be obtained. Thus, three possible orientationsdenoted respectively by a, b and c have been represented in FIG. 2.

A spring constituted by a Belleville washer 30 is interposed between thedifferential housing and the mobile sleeve 14b, and returns this sleevetowards the right when looking at FIG. 1.

Packing rings 31, 32 are also provided between this sleeve on the onehand and the housing and the shaft 16 on the other hand.

A controlled-slip coupling device or viscocoupler 33 is embedded insidethe housing 10 on the side of the side gear 14. This coupling device isof the type consisting of two alternating sets of discs, a first set 34being made to rotate solidly by splines on the output shaft 16associated with the side gear 14, while the other set of discs 35 ismade to rotate solidly by means of splines of the differential housing.These discs are immersed in a viscous fluid operating in shear, whichmay for example be a silicone oil. The vessel containing this fluid ispartly bounded by the end of the sleeve 14b.

Such a device operates as follows:

In the absence of engine torque, the coupling device 33 is only operatedor controlled by the difference in the rotational speeds between thehousing 10 and the output shaft 16 associated with the side gear 14.Since the characteristic Cv=f(Δn) is chosen to be fairly low (where Cvis the opposing torque due to the viscocoupler and Δn is the differencein the rotational speeds between the housing and the shaft 16), such adifferential offers little resistance to manoeuvres at very low speeds.

As soon as an effective engine torque is transmitted to the wheels,forces are exerted at the level of the ramps 26 and 27, thus producing adisplacement of the sleeve 14b towards the left. This displacement hasthe effect of reducing the volume offered to the viscous fluid in thevessel bounded by the housing 10, the shaft 16 and the end of the sleeve14b. This reduction in the volume of the vessel results in an increasein the internal fluid pressure and hence in a modification to thecharacteristic law Cv=f(Δn), which makes the viscocoupler more efficientin situations which are encountered when an engine torque is transmittedto the wheels.

When the torque is reversed and becomes a braking torque, it is thefaces 28, 29 which come into contact. If these faces are parallel to theaxis of rotation of the side gears (solution a in FIG. 2), the sleeve isnot acted upon so as to be displaced axially, except of course by thespring 30. The two other profiles b and c represented in FIG. 2, on thecontrary, produce a slight tendency for the sleeve to be displaced inone direction or the other, which may be desirable in certain cases.

In FIG. 3, there are several elements which are analogous to those inFIG. 1 and which are denoted by the same reference numbers. In thisvariant of the embodiment, the mobile part 14b of the side gear includesa radial flange 40 which bears on at least one shuttle 41 received in aboring 42 in the housing, which opens out into the viscocoupler vessel.

In addition, the means of connection between the two parts of the sidegear are here constituted by grooves 43 and lateral dog clutch teeth 44marking the boundary, as in the previous example, of the ramps 26, 27and 28, 29. These ramps are shown according to two variants in FIGS. 4Aand 4B. An elastic restoring component consisting of a Belleville washer45 is disposed in this case between the two components forming the sidegear and no longer between the differential housing and the mobile partof this side gear.

The operation of this device is wholly comparable with that describedpreviously, except for the difference that it is the displacement of theshuttle or of each shuttle which produces a variation in the volume andhence in the internal pressure of the viscocoupler.

According to another detail variant (FIG. 5), the shuttles 41 can bebrought to bear on a mobile plate 50 incorporated in the viscocouplerand capable of altering the separation between the discs of the saidviscocoupler.

FIG. 6 represents a mode of embodiment in which the invention is appliedto an inter-axle differential with an epicyclic gear train. The devicecomprises a housing 60 in which are disposed the differential 61, a discclutch 62 and a transmission mechanism with a timing belt 63 ensuringthe return towards a propeller shaft 64 connected to a front axle.

The differential includes a pinion-holder 65 which is connected to theinput shaft 66, a crown wheel 67 rotating solidly with a wheel disc 68and an output shaft 69 which forms a shaft for transmission to a rearaxle, and a side gear connected to a second output shaft 70 coaxial withthe input shaft and which is intended to drive the shaft 64 fortransmission to the front axle.

According to the invention, the side gear is made in two parts, a firstpart 71 mounted so that it is free to rotate on the shaft 70 and whichengages with the side pinions 65a, and a second part 72 which isrotating solidly because of splines on the output shaft 70 and whichconstitutes a thrust plate capable of acting on the clutch 62. Means forconnection to ramps 73, 74 similar to those described in connection withFIG. 3 are provided between the two parts 71 and 72 of the side gear.

The operation of such a device is analogous to that describedpreviously, except that the mobile part 72 of the side gear simply actsto control or operate a disc clutch and not to alter the operationalcharacteristic of a viscous-fluid coupling.

However, in this embodiment as in the previous ones, it is found that itis the torque passing in transit through the differential which, in asimple and reliable way, produces an action on a coupling associatedwith the differential. The means used are in fact particularly compactand cheap since it is sufficient in all cases to make an output elementof the differential in two parts and to provide between these two partsramps which have the effect of displacing the mobile part of the saidoutput element axially over a predetermined distance. Such a solution isparticularly attractive in that it means that no changes are needed inthe gearing conditions of the output element in question, since the partof this element which cooperates with the other components of thedifferential is fixed axially, so that the usual sets of teeth arepreserved, thus guaranteeing reliable and silent operation.

The operation of a device according to the invention is illustrated inFIG. 7 where a C/Δn diagram shows the characteristics of knownsolutions, of the solution according to the invention and of an "ideal"solution denoted by the reference letter A. The curves B1 and B2correspond to solutions of the friction clutch type for two differentratings. The curves C1, C2, C3 illustrate three characteristics of knownviscocoupler devices. The curve D corresponds to the use of theinvention applied to the control of a viscocoupler, and it can be seenthat it passes progressively, under an engine torque, from the basiccharacteristic C1 to the extreme characteristic C3, the end part of thecurve D corresponding to the coming into play of stops, which limit theaxial displacement of the mobile sleeve.

The lower part of the diagram illustrates what happens during operationwith engine braking. If the ramps which are involved in this operationalsituation are parallel to the X--X axis, a characteristic C'1symmetrical to the characteristic C1 is obtained. It is even possible toobtain a characteristic D' weaker than C'1 if the ramps have an undercutprofile as shown in FIGS. 2 and 4B.

It should also be noted that, in the application to a deviceincorporating a viscocoupler, the invention allows the phenomenon ofviscocoupler locking to occur under the effect of an increase inpressure, itself resulting from an increase in temperature, thisphenomenon being very frequently sought in order to be able to startunder extreme limiting conditions of poor road-holding.

I claim:
 1. A transmission device comprising:a differential having ahousing (10;60), an input element and a first and second output element,said first output element of the differential being made in two parts; afirst part (14a;71) of said two parts of said first output elementhaving teeth in meshing engagement with at least one other component ofthe differential, said first part further defining a radial surface inaxial abutment against an adjacent radial surface which is fixed withrespect to said input element; a second part (14b; 72) of said two partsof said first output element being axially movable over a limiteddistance; said second part being connected to rotate with an outputshaft; a coupling device (33; 62) being disposed between said outputshaft and one of said housing, said input element or said second outputelement; and means (24,25; 43,44; 73,74) provided between said firstpart and said second part of said first output element for allowing alimited angular movement between them such that a relative angulardisplacement between said first and second part in at least onedirection under the effect of a torque provides for an axialdisplacement of the second part, said axial displacement modifying anoperating condition of the coupling device.
 2. Device according to claim1 wherein said first part (14a) abuts one face (22) of the differentialhousing.
 3. Device according to claim 1 wherein said first part (71)bears against one face (22) of a pinion-holder (65) forming part of thedifferential.
 4. Device according to claim 1 wherein said means comprisea first set of ramps (26, 27) inclined with respect to the direction ofthe (X--X) axis of the first output element, said first set of rampsengaging each other when a driving torque is transmitted by thedifferential.
 5. Device according to claim 4 wherein said means comprisea second set of ramps (28, 29) which engage each other when a brakingtorque is transmitted by the differential.
 6. Device according to claim5 wherein said second set of ramps (28, 29) are oriented parallel to the(X--X) axis of said first output element.
 7. Device according to claim 5wherein said second set of ramps (28, 29) are inclined with respect tothe direction of the (X--X) axis of said first output element.
 8. Deviceaccording to claim 1 wherein said first output element is a side gear.9. Device according to claim 8 wherein said second part of the side gearincorporates a sleeve (14b) connected by splines to the output shaft(16; 70).
 10. Device according to claim 9 wherein said sleeve (14b)extends concentrically inside the first part (14a) of the side gear. 11.Device according to claim 9 wherein the sleeve (14b) includes a radialflange (40) which bears against at least one shuttle (41) slidingaxially in a bore (42) in the housing.
 12. Device according to claim 9wherein the sleeve incorporates a pressure plate (72) cooperating withthe coupling device (62).
 13. Device according to claim 1 wherein areturn spring (30) in interposed between the housing (10) and the secondpart (14b) of the first output element.
 14. Device according to claim 1wherein a return spring (45) is interposed between the first and secondparts (14a, 14b) of the first output element.
 15. Device according toclaim 1 wherein the coupling device is a friction clutch (62) and thesecond part of the first output element acts to control the frictionclutch.
 16. A device according to claim 15 wherein said coupling devicecomprises two alternating sets of discs cooperating respectively withtwo distinct components of the second part of the first output element.17. Device according to claim 1 wherein the coupling device is aviscocoupler and the second part of the first output element acts toalter the operational characteristics of the viscocoupler.
 18. A deviceaccording to claim 17 wherein said coupling device comprises twoalternating sets of discs operating respectively with two distinctcomponents of said second part of said first output element.